1 /* 2 * Resizable simple ram filesystem for Linux. 3 * 4 * Copyright (C) 2000 Linus Torvalds. 5 * 2000 Transmeta Corp. 6 * 7 * Usage limits added by David Gibson, Linuxcare Australia. 8 * This file is released under the GPL. 9 */ 10 11 /* 12 * NOTE! This filesystem is probably most useful 13 * not as a real filesystem, but as an example of 14 * how virtual filesystems can be written. 15 * 16 * It doesn't get much simpler than this. Consider 17 * that this file implements the full semantics of 18 * a POSIX-compliant read-write filesystem. 19 * 20 * Note in particular how the filesystem does not 21 * need to implement any data structures of its own 22 * to keep track of the virtual data: using the VFS 23 * caches is sufficient. 24 */ 25 26 #include <linux/fs.h> 27 #include <linux/pagemap.h> 28 #include <linux/highmem.h> 29 #include <linux/time.h> 30 #include <linux/init.h> 31 #include <linux/string.h> 32 #include <linux/backing-dev.h> 33 #include <linux/ramfs.h> 34 #include <linux/sched.h> 35 #include <linux/parser.h> 36 #include <linux/magic.h> 37 #include <linux/slab.h> 38 #include <linux/uaccess.h> 39 #include <linux/fs_context.h> 40 #include <linux/fs_parser.h> 41 #include "internal.h" 42 43 struct ramfs_mount_opts { 44 umode_t mode; 45 }; 46 47 struct ramfs_fs_info { 48 struct ramfs_mount_opts mount_opts; 49 }; 50 51 #define RAMFS_DEFAULT_MODE 0755 52 53 static const struct super_operations ramfs_ops; 54 static const struct inode_operations ramfs_dir_inode_operations; 55 56 struct inode *ramfs_get_inode(struct super_block *sb, 57 const struct inode *dir, umode_t mode, dev_t dev) 58 { 59 struct inode * inode = new_inode(sb); 60 61 if (inode) { 62 inode->i_ino = get_next_ino(); 63 inode_init_owner(&init_user_ns, inode, dir, mode); 64 inode->i_mapping->a_ops = &ram_aops; 65 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); 66 mapping_set_unevictable(inode->i_mapping); 67 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); 68 switch (mode & S_IFMT) { 69 default: 70 init_special_inode(inode, mode, dev); 71 break; 72 case S_IFREG: 73 inode->i_op = &ramfs_file_inode_operations; 74 inode->i_fop = &ramfs_file_operations; 75 break; 76 case S_IFDIR: 77 inode->i_op = &ramfs_dir_inode_operations; 78 inode->i_fop = &simple_dir_operations; 79 80 /* directory inodes start off with i_nlink == 2 (for "." entry) */ 81 inc_nlink(inode); 82 break; 83 case S_IFLNK: 84 inode->i_op = &page_symlink_inode_operations; 85 inode_nohighmem(inode); 86 break; 87 } 88 } 89 return inode; 90 } 91 92 /* 93 * File creation. Allocate an inode, and we're done.. 94 */ 95 /* SMP-safe */ 96 static int 97 ramfs_mknod(struct user_namespace *mnt_userns, struct inode *dir, 98 struct dentry *dentry, umode_t mode, dev_t dev) 99 { 100 struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev); 101 int error = -ENOSPC; 102 103 if (inode) { 104 d_instantiate(dentry, inode); 105 dget(dentry); /* Extra count - pin the dentry in core */ 106 error = 0; 107 dir->i_mtime = dir->i_ctime = current_time(dir); 108 } 109 return error; 110 } 111 112 static int ramfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir, 113 struct dentry *dentry, umode_t mode) 114 { 115 int retval = ramfs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0); 116 if (!retval) 117 inc_nlink(dir); 118 return retval; 119 } 120 121 static int ramfs_create(struct user_namespace *mnt_userns, struct inode *dir, 122 struct dentry *dentry, umode_t mode, bool excl) 123 { 124 return ramfs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0); 125 } 126 127 static int ramfs_symlink(struct user_namespace *mnt_userns, struct inode *dir, 128 struct dentry *dentry, const char *symname) 129 { 130 struct inode *inode; 131 int error = -ENOSPC; 132 133 inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0); 134 if (inode) { 135 int l = strlen(symname)+1; 136 error = page_symlink(inode, symname, l); 137 if (!error) { 138 d_instantiate(dentry, inode); 139 dget(dentry); 140 dir->i_mtime = dir->i_ctime = current_time(dir); 141 } else 142 iput(inode); 143 } 144 return error; 145 } 146 147 static int ramfs_tmpfile(struct user_namespace *mnt_userns, 148 struct inode *dir, struct dentry *dentry, umode_t mode) 149 { 150 struct inode *inode; 151 152 inode = ramfs_get_inode(dir->i_sb, dir, mode, 0); 153 if (!inode) 154 return -ENOSPC; 155 d_tmpfile(dentry, inode); 156 return 0; 157 } 158 159 static const struct inode_operations ramfs_dir_inode_operations = { 160 .create = ramfs_create, 161 .lookup = simple_lookup, 162 .link = simple_link, 163 .unlink = simple_unlink, 164 .symlink = ramfs_symlink, 165 .mkdir = ramfs_mkdir, 166 .rmdir = simple_rmdir, 167 .mknod = ramfs_mknod, 168 .rename = simple_rename, 169 .tmpfile = ramfs_tmpfile, 170 }; 171 172 /* 173 * Display the mount options in /proc/mounts. 174 */ 175 static int ramfs_show_options(struct seq_file *m, struct dentry *root) 176 { 177 struct ramfs_fs_info *fsi = root->d_sb->s_fs_info; 178 179 if (fsi->mount_opts.mode != RAMFS_DEFAULT_MODE) 180 seq_printf(m, ",mode=%o", fsi->mount_opts.mode); 181 return 0; 182 } 183 184 static const struct super_operations ramfs_ops = { 185 .statfs = simple_statfs, 186 .drop_inode = generic_delete_inode, 187 .show_options = ramfs_show_options, 188 }; 189 190 enum ramfs_param { 191 Opt_mode, 192 }; 193 194 const struct fs_parameter_spec ramfs_fs_parameters[] = { 195 fsparam_u32oct("mode", Opt_mode), 196 {} 197 }; 198 199 static int ramfs_parse_param(struct fs_context *fc, struct fs_parameter *param) 200 { 201 struct fs_parse_result result; 202 struct ramfs_fs_info *fsi = fc->s_fs_info; 203 int opt; 204 205 opt = fs_parse(fc, ramfs_fs_parameters, param, &result); 206 if (opt < 0) { 207 /* 208 * We might like to report bad mount options here; 209 * but traditionally ramfs has ignored all mount options, 210 * and as it is used as a !CONFIG_SHMEM simple substitute 211 * for tmpfs, better continue to ignore other mount options. 212 */ 213 if (opt == -ENOPARAM) 214 opt = 0; 215 return opt; 216 } 217 218 switch (opt) { 219 case Opt_mode: 220 fsi->mount_opts.mode = result.uint_32 & S_IALLUGO; 221 break; 222 } 223 224 return 0; 225 } 226 227 static int ramfs_fill_super(struct super_block *sb, struct fs_context *fc) 228 { 229 struct ramfs_fs_info *fsi = sb->s_fs_info; 230 struct inode *inode; 231 232 sb->s_maxbytes = MAX_LFS_FILESIZE; 233 sb->s_blocksize = PAGE_SIZE; 234 sb->s_blocksize_bits = PAGE_SHIFT; 235 sb->s_magic = RAMFS_MAGIC; 236 sb->s_op = &ramfs_ops; 237 sb->s_time_gran = 1; 238 239 inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0); 240 sb->s_root = d_make_root(inode); 241 if (!sb->s_root) 242 return -ENOMEM; 243 244 return 0; 245 } 246 247 static int ramfs_get_tree(struct fs_context *fc) 248 { 249 return get_tree_nodev(fc, ramfs_fill_super); 250 } 251 252 static void ramfs_free_fc(struct fs_context *fc) 253 { 254 kfree(fc->s_fs_info); 255 } 256 257 static const struct fs_context_operations ramfs_context_ops = { 258 .free = ramfs_free_fc, 259 .parse_param = ramfs_parse_param, 260 .get_tree = ramfs_get_tree, 261 }; 262 263 int ramfs_init_fs_context(struct fs_context *fc) 264 { 265 struct ramfs_fs_info *fsi; 266 267 fsi = kzalloc(sizeof(*fsi), GFP_KERNEL); 268 if (!fsi) 269 return -ENOMEM; 270 271 fsi->mount_opts.mode = RAMFS_DEFAULT_MODE; 272 fc->s_fs_info = fsi; 273 fc->ops = &ramfs_context_ops; 274 return 0; 275 } 276 277 static void ramfs_kill_sb(struct super_block *sb) 278 { 279 kfree(sb->s_fs_info); 280 kill_litter_super(sb); 281 } 282 283 static struct file_system_type ramfs_fs_type = { 284 .name = "ramfs", 285 .init_fs_context = ramfs_init_fs_context, 286 .parameters = ramfs_fs_parameters, 287 .kill_sb = ramfs_kill_sb, 288 .fs_flags = FS_USERNS_MOUNT, 289 }; 290 291 static int __init init_ramfs_fs(void) 292 { 293 return register_filesystem(&ramfs_fs_type); 294 } 295 fs_initcall(init_ramfs_fs); 296